M48T86_YEAR
m48t86_writeb(dev, tm->tm_year % 100, M48T86_YEAR);
m48t86_writeb(dev, bin2bcd(tm->tm_year % 100), M48T86_YEAR);
tm->tm_year = m48t86_readb(dev, M48T86_YEAR) + 100;
tm->tm_year = bcd2bin(m48t86_readb(dev, M48T86_YEAR)) + 100;